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Old Feb 20, 2013, 10:01 AM
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Te edge shaping advice

New to building andthis is a wing from a semi scale bi-plane.The ribs end short of the trailing edge.this is how the plan shows the ribs.How do i finish the TE . leave it square or round it. And how does the covering fabric get attached at the rib/te area because of the step from rib to te.
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Old Feb 20, 2013, 11:20 AM
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Are you saying that there is nothing covering the top of the ribs at the trailing edge?

What kit, by the way?

EJWash
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Old Feb 20, 2013, 12:26 PM
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I would leave it square and wrap the covering to the underside of the T.E., you can lightly sand the T.E. so its not as a pronounced step from rib to T.E.
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Old Feb 20, 2013, 02:10 PM
Dr John
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Sand the TE following the rib shape to a sharp back edge.
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Old Feb 20, 2013, 03:41 PM
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Use the blue tape method to sand the TE. See Hobby Lobby Senior Telemaster information to see what that is and how it works. Much better than me trying to explain it here.

L.
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Old Feb 20, 2013, 04:56 PM
B for Bruce
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Yep, sand a narrow wedge along the edge so the line of the ribs is extended to the edge of the TE wood. It'll likely still have some thickness. You want to leave it squared. It's a cleaner exit point for the airflow that way.
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Old Feb 20, 2013, 05:16 PM
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I think its only pertinent to see if the OP's model has a covered trailing edge or not, and then make suggestions. From the pic, the rear top spar isn't even installed, and there may be cap strips involved. let's make sure what we have here.

EJWash
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Old Feb 20, 2013, 05:42 PM
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Quote:
Originally Posted by EJWash1 View Post
I think its only pertinent to see if the OP's model has a covered trailing edge or not, and then make suggestions. From the pic, the rear top spar isn't even installed, and there may be cap strips involved. let's make sure what we have here.

EJWash


Yep.. not much to go on there. What do the plans tell tell us? A pic of the wing root portion on the plan might tell 1000 tales here... and without knowing even what model we're looking at, I didn't see a particular model mentioned.... other then a "semi-scale bipe"... sky's the limit on how it "should" be.. its ok though...... you can tell us.... the more info you can give... the more info you'll receive.

Theres an awful lot of speculation on how it should finish though.... I find that interesting.. as for 10 modelers.. theres 10 ways it could finish.. haha.. its all good though.. I usually prefer to start with the plans, then work it out from there.. but... thats just me.
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Old Feb 21, 2013, 03:01 AM
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Sorry for the delay in replying.The TE is bottom section only ,no top strip is used,just open structure.
You are correct in that no gluing of ribs asa been done yet.I was waiting to see if the correct method would need me to cut the TE back to the rib ends.On the semiscale sop pup i do not know if the TE is better left sq with some thickness or chamfered down.not worried about scaale apperance just longevity.
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Old Feb 21, 2013, 07:16 AM
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Quote:
Originally Posted by rubble View Post
Sorry for the delay in replying.The TE is bottom section only ,no top strip is used,just open structure.
You are correct in that no gluing of ribs asa been done yet.I was waiting to see if the correct method would need me to cut the TE back to the rib ends.On the semiscale sop pup i do not know if the TE is better left sq with some thickness or chamfered down.not worried about scaale apperance just longevity.
Okay, now we have a better idea of what's going on.

Being that the ribs end before the trailing edge, this gives you room to taper the top of the trailing edge to meet the contour of the rib profile. Personally, I would not leave the trailing edge with a sharp finished edge because it would be very susceptible to dents and rashes. I'd give it a subtle rounded-over finish. We're talking a Sopwith Pup here, not an F-104. I've never done it, but you could also give the finished trailing edge some durability by running some CA over it to harden it.

EJWash
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Old Feb 21, 2013, 08:43 AM
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Quote:
Originally Posted by EJWash1 View Post
Okay, now we have a better idea of what's going on.

but you could also give the finished trailing edge some durability by running some CA over it to harden it.

EJWash
I've used 1/64 ply strips to harden a TE before. They were laminated in the joint of top and bottom sheeting though. I would think just laminated on the top, under the ribs, would give the same effect.

Ken
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Old Feb 21, 2013, 12:38 PM
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Guys, I strongly suspect that this is either a rubber power model or intended to be a free flight rubber power like airframe for use as an RC parkflyer. In fact I would not be surprised to learn from Rubble that this is a Guillows kit conversion. This style is very typical of Guillows model designs.

As such lightness counts for much and the covering used will be one of the lighter style films or perhaps even tissue, dope and airbrush misted on enamel colouring.

If this is accurate then adding reinforcements that add to the weight isn't a good option if it isn't needed. And the final model is going to be such that care will be needed during ground handling and transport anyway.

Rubble, here's what I was describing above. Given your rib coverage over the sheet trailing edge sanding down the trailing edge strip as shown by the red line will still result in a reasonably stout and hard enough squared off edge. Ideally such edges ON THE TRAILING EDGES are left square. But rounding over the extreme edge after you remove that indicated red line portion isn't the end of the world either.

A hint for you. If you are going to cover with tissue and dope then a little candle wax rubbed on the upper flat area between the ribs will aid in preventing the tissue sticking to the wood other than at the proper sanded and shaped extreme edge. Long time Guillows builders or folks that have built and covered models with this same style of trailing edge will know that without such a trick that the dop often sticks the tissue to this area and results in odd looking covering.
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Old Feb 21, 2013, 01:43 PM
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BMatthews,

Exactly why I don't like trying to help until I know what model is involved. Questions about general techniques is one thing, but when there is a specific model involved, it's easy to go down the wrong road with advice.

Been a long time since I built a stick-and-tissue model - more than forty-five years. Where were you back then with that candle wax trick? I needed it!

The OP's Pup looks like a laser kit.

EJWash
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Old Feb 23, 2013, 07:47 AM
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Hey BMATTHEWS, I been building em since the 60's & could have used that candle wax idea more than once! Thats one to file away to try someday for sure. THANKS.....Gene
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Old Feb 23, 2013, 09:41 PM
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Along with B Matthews' suggestion, is the crayon anti-stick solution........I used to use tan Crayolas till they told me to "grow up".
I didn't think 17 was too old....
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